Common rail fuel systems typically employ multiple closed-nozzle fuel injectors to inject high pressure fuel into the combustion chambers of an engine. Each of these fuel injectors include a nozzle assembly having a cylindrical bore with a nozzle supply passageway and a nozzle outlet. A needle check valve is reciprocatingly disposed within the cylindrical bore and biased toward a closed position where the nozzle outlet is blocked. To inject fuel, the needle check valve is selectively moved to open the nozzle outlet, thereby allowing high pressure fuel to flow from the nozzle supply passageway into the combustion chamber. To move the needle check valve, a control chamber in fluid communication with a base of the needle check valve is selectively drained of pressurized fuel to create a force imbalance that biases the needle check valve toward the open position.
A piezo actuator is often used to drain the pressurized fuel from the base of the needle check valve. Specifically, the piezo actuator, upon being energized, expands to move a valve element from a first position at which pressurized fuel is directed to the base of the needle check valve, to a second position at which the pressurized fuel at the base of the needle check valve is directed to a drain. Although this configuration is effective for initiating the injection of fuel, it is critical that the piezo actuator remain isolated and protected from the fuel and other contaminates. In particular, fuel, if allowed to contact the piezo actuator, can short circuit the actuator or otherwise degrade the performance of the actuator.
One method utilized by injector manufacturers to isolate the actuator from fuel and other contaminates is described in U.S. Pat. No. 6,874,475 (the '475 patent) issued to Katsura et al. on Apr. 5, 2005. The '475 patent describes a fuel injector for an internal combustion engine. The fuel injector includes a piezo electric valve actuator enclosed within a housing. The housing is made of stainless steel cylindrical bellows consisting of large-diameter portions and small-diameter portions arrayed alternately. The bellows allow expansion and contraction of the piezo electric valve actuator through deformation. The housing is hermetically closed by an upper plate and a lower plate to minimize the ingress of fuel. The upper and lower plates are used to transfer force imparted by the piezo electric valve actuator. One of the lower and upper plates may be formed integral with the housing to improve air tightness.
Although the fuel injector of the '475 patent may sufficiently inject fuel while minimizing piezo/fuel contamination, it may be problematic and costly. For example, because the one of the lower and upper plates and the housing are integral, the material of both the plate and the housing must be the same. This material, when optimized for the deformation described above, may not be optimal for force transmission. Similarly, this material, when optimized for the force transmission described above, may deform poorly. Components fabricated from material that is not optimally suited for intended operations may be prone to premature failure. In addition, because a first material used, for example, to fabricate the housing, may have a higher cost than a second material best suited for the plate, the integral component functioning as both the housing and the plate, which is made of only the first material may unnecessarily increase the cost of the fuel injector. Further, the process of fabricating this integral housing/plate component may be expensive.
The fuel injector of the present disclosure solves one or more of the problems set forth above.